From 319bffddc2e4467fc00efa0a19cf8f2472f3158e Mon Sep 17 00:00:00 2001
From: John Hodge <tpg@ucc.asn.au>
Date: Sun, 10 Sep 2017 22:20:24 +0800
Subject: Const Eval - Evalulate from MIR where possible (avoids BorrowData)

---
 src/hir_expand/const_eval_full.cpp | 20 ++++++++++++++------
 src/trans/codegen_c.cpp            |  4 ++--
 2 files changed, 16 insertions(+), 8 deletions(-)

(limited to 'src')

diff --git a/src/hir_expand/const_eval_full.cpp b/src/hir_expand/const_eval_full.cpp
index b3f5bf1e..4fd10c05 100644
--- a/src/hir_expand/const_eval_full.cpp
+++ b/src/hir_expand/const_eval_full.cpp
@@ -408,13 +408,21 @@ namespace {
                 // TODO: Monomorph the path? (Not needed... yet)
                 auto ent = get_ent_fullpath(sp, resolve.m_crate, e2.p, EntNS::Value,  const_ms);
                 ASSERT_BUG(sp, ent.is_Constant(), "MIR Constant::Const("<<e2.p<<") didn't point to a Constant - " << ent.tag_str());
-                auto val = clone_literal( ent.as_Constant()->m_value_res );
-                if( val.is_Invalid() ) {
+                const auto& c = *ent.as_Constant();
+                // Prefer re-evaluating the MIR.
+                // - Constants insert themselves directly, so this is
+                //   effectively the same thing.
+                // Avoids _BorrowData leftovers.
+                if( c.m_value ) {
                     return evaluate_constant(sp, resolve, newval_state, FMT_CB(ss, ss << e2.p;), ent.as_Constant()->m_value, {}, {});
                 }
-                // Monomorphise the value according to `const_ms`
-                monomorph_literal_inplace(sp, val, const_ms);
-                return val;
+                else {
+                    auto val = clone_literal( ent.as_Constant()->m_value_res );
+                    ASSERT_BUG(sp, !val.is_Invalid(), "MIR Constant::Const("<<e2.p<<") pointed to invalid Constant - (no mir, no literal)");
+                    // Monomorphise the value according to `const_ms`
+                    monomorph_literal_inplace(sp, val, const_ms);
+                    return val;
+                }
                 ),
             (ItemAddr,
                 return ::HIR::Literal::make_BorrowPath( ms.monomorph(sp, e2) );
@@ -477,7 +485,7 @@ namespace {
                     if( const auto* p = e.val.opt_Deref() ) {
                         if( p->val->is_Deref() )
                             MIR_TODO(state, "Undo nested deref coercion - " << *p->val);
-                        val =  read_lval(*p->val);
+                        val = read_lval(*p->val);
                     }
                     else if( const auto* p = e.val.opt_Static() ) {
                         // Borrow of a static, emit BorrowPath with the same path
diff --git a/src/trans/codegen_c.cpp b/src/trans/codegen_c.cpp
index e8643591..b942dae7 100644
--- a/src/trans/codegen_c.cpp
+++ b/src/trans/codegen_c.cpp
@@ -1596,7 +1596,7 @@ namespace {
                 m_of << Trans_Mangle( params.monomorph(m_resolve, e));
                 ),
             (BorrowData,
-                MIR_TODO(*m_mir_res, "Handle BorrowData - " << *e);
+                MIR_TODO(*m_mir_res, "Handle BorrowData (emit_literal) - " << *e);
                 ),
             (String,
                 m_of << "{ ";
@@ -4096,7 +4096,7 @@ namespace {
                 }
                 ),
             (BorrowData,
-                MIR_TODO(*m_mir_res, "Handle BorrowData - " << *e);
+                MIR_TODO(*m_mir_res, "Handle BorrowData (assign_from_literal) - " << *e);
                 ),
             (String,
                 emit_dst(); m_of << ".PTR = ";
-- 
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